This invention relates to ablation devices that are used to create lesions in tissue. More particularly, this invention relates to conductive elements for use in such devices which vary in length and which incorporate improved methods of irrigation delivery.
The action of the heart is known to depend on electrical signals within the heart tissue. Occasionally, these electrical signals do not function properly. The maze procedure is a surgical operation for patients with chronic atrial fibrillation that is resistant to medical treatment. In this procedure, incisions are created in the right and left atria to produce an orderly passage of the electrical impulse from the SA node to the atrioventricular node. Blind passageways are also created to suppress reentry cycles. Currently, the lesions may still be created using a traditional cut and sew technique. The scar tissue resulting from the procedure results in a non-conductive lesion.
Ablation of cardiac conduction pathways in the region of tissue where the signals are malfunctioning is now being used to replace the surgical incisions. Ablation is also used therapeutically with other organ tissue, such as the liver, prostate and uterus. Ablation of organic tissue is also used in several surgical procedures, for both diagnosis and therapy.
In one type of procedure, one or more electrodes at the tip of an electrophysiology ablation device allow the physician to measure electrical signals along the surface of the heart (mapping). When necessary, in another type of procedure, the physician can also ablate certain tissues using, typically, radio frequency (RF) energy conducted to one or more ablation electrodes. During tissue ablation, energy is used to create lesions in the tissue for different purposes. High levels of energy are used to cut and remove tissue (electrosurgery). Lower levels of energy are used to cause cell damage but leave the structure intact so that electrical pathways are blocked within the tissue.
A variety of devices, such as catheters, are used to ablate tissue. Typically, such devices include a conductive tip, which serves as one electrode in an electrical circuit. The electrical circuit is completed via a grounding electrode that may also be on the device or may be coupled to the patient. By controlling the level of energy transmitted to the electrode, the surgeon is able to control the amount of heat generated for the purposes described above.
Irrigation of the ablation site cools the electrode. Irrigated ablation is also known to create deeper lesions that are more likely to be transmural. Transmurality is achieved when the full thickness of the target tissue is ablated.
During ablation, irrigation of the ablation site helps to cool the ablation electrodes, thereby reducing overheating in the vicinity of the electrodes. Undesirable consequences of overheating include the excessive coagulation of blood and the unintended destruction of healthy tissue adjacent the ablation site. The efficient cooling of the linear ablation electrode permits longer lesions to be created by permitting higher ablation energy without resulting in excessive electrode heating.
Typically, delivery of irrigation to the site is accomplished using a separate irrigation source which may pump into the ablation device or which may pump directly to the target tissue site. This requires a separate device that may not deliver irrigation as site-specifically as desired.
Furthermore, there is relatively high hydraulic impedance to saline flow at the distal end (towards ablation site) of a typical ablation device. In comparison, the hydraulic impedance to flow is lower at the proximal end (towards user) of the device. This sometimes results in more irrigation fluid being distributed at the proximal end than at the distal end.
Additionally, there may also be difficulties with electrical impedance to saline flow in a typical ablation device. This may be particularly true in a hemostat-type ablation device. In such a device, the target tissue is positioned between the two jaws of the hemostat, both of which carry ablation electrodes. If the tissue is shorter than the length of the hemostat jaws, a saline bridge may form between the hemostat jaws due to the surface tension of the fluid. This saline bridge is a low electrical impedance pathway. Electrical flow may, therefore, occur preferentially towards the bridge and yield unreliable ablation.
Irrigation fluid may also not be evenly distributed along a single electrode because of the impedance factors described above. Uneven distribution of fluid may result in an uneven lesion. In some cases, the tissue may not receive any irrigation in some areas. The electrode may contact the surface of the target tissue in these unirrigated areas, causing sticking or even charring.
Additionally, longer electrodes are sometimes desired to create longer lesions. These electrodes have a larger pressure drop along their length. This results in greater fluid flow from the proximal end than the distal end and thus irrigation is unevenly distributed which may result in sticking of the ablated tissue to the electrode. Currently an electrode of a given length is needed to create a lesion of a given length. If a lesion of a different length is desired, a new electrode must be used.
It would be desirable therefore to provide a means to control and vary irrigation.
It would further be desirable to facilitate control of lesion length.
It would further be desirable to provide a means for evenly irrigating an ablation electrode and concomitant target tissue site.
It would further be desirable to provide a means for evenly irrigating ablation electrodes of variable length.
It would further be desirable to provide a device in which irrigation capabilities and ablation capabilities are integrated.
One aspect of the present invention provides a device for ablating organic tissue. The device includes a conductive element, a fluid component in communication with the conductive element and a non-conductive interface positioned adjacent the tissue to allow the fluid to pass through the interface and contact the tissue. The conductive element may be, for example, a metallic coil with a lumen, a spring with a lumen or a wire. The diameter of the conductive element may be greater than the diameter of the interface. The conductive element and the interface may be the same. The interface may be microporous. The interface may also be of a variable length and a portion of the interface may be removable. The interface may be perforated, may comprise openings that are slidably or rotatably opened. The interface may be non-conductive or conductive. The interface may lie between the conductive element and the tissue surface. The interface may encircle the conductive element and the fluid component. The interface may be a rigid structure, a fluid saturated gel, or a microporous section of the fluid component. The interface and the fluid component may be the same. The fluid component may be a non-porous coating. The device may also include means for flowing the fluid component through the interface, such as an infusion pump.
Another aspect of the invention provides a device for creating ablations of variable length, comprising a conductive element having a channel formed therein, the channel operatively adapted to receive irrigating fluid; and a removable non-conductive interface in communication with the conductive element. The device may include a support element in communication with the conductive element. The support element may be a slotted tube. The conductive element may be a slotted tube.
Another aspect of the invention provides a device for creating ablations of variable length, comprising a non-porous tube operatively adapted to receive irrigating fluid therein, a conductive element in communication with the tube and a removable non-conductive interface in communication with the conductive element. The non-conductive interface may be a portion of the non-porous tube. The non-conductive interface may be micro-porous. The non-conductive interface may be rigid.
Another aspect of the present invention provides a device for creating ablations of variable length, comprising a non-porous tube operatively adapted to receive a hydrogel, a conductive element in communication with the tube and a removable non-conductive interface in communication with the conductive element. The non-porous tube may be slotted.
Another aspect of the present invention provides a method of ablating organic tissue. The method includes providing a conductive element having a channel formed therein, the channel operatively adapted to receive irrigating fluid; and a removable non-conductive interface in communication with the conductive element. The method also includes removing a portion of the interface to expose a portion of the conductive element and ablating the tissue with the exposed portion of the conductive element. The interface may be perforated. The interface may be disposable. The interface may be reusable. The interface may also be a removable tip.
The foregoing, and other, features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims in equivalence thereof.